Signal compressing signal

ABSTRACT

A multi-scanner scans a signal according to several different patterns. A scanning pattern selector determines which scanning pattern produced the most efficient coding result, for example, for runlength coding, and outputs a coded signal, coded most efficiently, and a selection signal which identifies the scanning pattern found to be most efficient.

FIELD OF THE INVENTION

[0001] The present invention relates to a signal compressing system. Asystem according to the present invention is particularly suited forcompressing image signals. The present disclosure is based on thedisclosure in Korean Patent Application No. 92-3398 filed Feb. 29, 1992,which disclosure is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Image signals may be compressed by motion-compensated interframediscrete cosine transform (DCT) coding such as is defined by a MPEG(Moving Picture Expert Group) international standard. This form ofsignal compression has attracted much attention in the field of highdefinition television (HDTV).

[0003]FIG. 1 is a block diagram of such a conventionalmotion-compensated interframe DCT coder. In the shown coder, an imagesignal is divided into a plurality of sub-blocks. The sub-blocks are allof the same size, for example 8×8, 16×16, . . . . A motion estimator 40produces a motion vector, defined by the difference between the currentimage signal and a one-frame delayed image signal, output by a framememory 30. The motion vector is supplied to a motion compensator 50which compensates the delayed image signal from the frame memory 30 onthe basis of the motion vector. A first adder 8 a serves to produce thedifference between the present frame and the delayed, motion compensatedframe. A discrete cosine transform portion 10 processes the differencesignal, output by the first adder 8 a, for a sub-block. The motionestimator 40 determines the motion vector by using a block matchingalgorithm.

[0004] The discrete cosine transformed signal is quantized by aquantizer 20. The image signal is scanned in a zig-zag manner to producea runlength coded version thereof. The runlength coded signal comprisesa plurality of strings which include a series of “0”s, representing therun length, and an amplitude value of any value except “0”.

[0005] The runlength coded signal is dequantized by a dequantizer 21,inversely zig-zag scanned and inversely discrete cosine transformed byan inverse discrete cosine transforming portion 11. The transformedimage signal is added to the motion-compensated estimate error signal bya second adder 8 b. As a result the image signal is decoded into asignal corresponding to the original image signal.

[0006] Refresh switches RSW1, RSW2 are arranged between the adders 8 a,8 b and the motion compensator 40 so as to provide the original imagesignal free from externally induced errors.

[0007] The runlength coded signal is also supplied to a variable lengthcoder 60 which applies a variable length coding to the runlength codedimage signal. The variable length coded signal is then output through aFIFO transfer buffer 70 as a coded image signal.

[0008] In motion-compensated adaptive DCT coding, the interframe signalcan be easily estimated or coded by way of motion compensation, therebyobtaining a high coding efficiency, since the image signal has arelatively high correlation along the time axis. That is, according tothe afore-mentioned method, the coding efficiency is high because mostof the energy of a discrete cosine transformed signal is compressed atthe lower end of its spectrum, resulting in long runs of “0”s in therunlength coded signal.

[0009] However, the scanning regime of the afore-mentioned method doesnot take account of differences in the spectrum of themotion-compensated interframe DCT signal with time.

[0010] A method is known wherein one of a plurality of reference modesis previously selected on the basis of the difference between thepresent block and that of a previous frame and the image signal isscanned by way of a scanning pattern under the selected mode andsuitably quantized. With such a method, however, three modes areemployed to compute the energies of the intermediate and high frequencycomponents of the image signal in accordance with the interframe or theintraframe modes in order to determine the appropriate mode. This modedetermining procedure is undesirable complicated.

SUMMARY OF THE INVENTION

[0011] According to the present invention, there is provided a signalcompressing system, comprising coding means for scanning an input signalaccording to a plurality of different scanning patterns to providedcoded versions thereof and selection means for selecting a said scanningpattern which produces efficient coding according to a predeterminedcriterion and outputting a scanning pattern signal identifying theselected scanning pattern.

[0012] Preferably, the input signal is an inherently two-dimensionalsignal, for example, an image signal.

[0013] Preferably, the coding means codes the input signal according toa runlength coding regime.

[0014] Preferably, the system includes a variable length coder tovariably length code the coded signal, produced by scanning according tothe selected scanning pattern.

[0015] Preferably, the system includes discrete cosine transformer meansto produce said input signal. The transformer means may be amotion-compensated interframe adaptive discrete cosine transformer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] An embodiment of the present invention will now be described, byway of example, with reference to FIGS. 2 and 3 of the accompanyingdrawings, in which:

[0017]FIG. 1 is a block diagram of a conventional adaptive interframeDCT coding system employing a motion compensating technique;

[0018]FIG. 2 is a block diagram of a coding system embodying the presentinvention; and

[0019] FIGS 3A-3H shows various possible scanning patterns according tothe present invention.

Detailed Description of the Preferred Embodiments

[0020] Referring to FIG. 2, an input signal is divided into equal-sizedsub-blocks, for example, 8×8, 16×16, . . . . A motion estimator 40determines a motion vector by comparing the current frame and a oneframe delayed signal from a frame memory 30.

[0021] The motion vector is supplied to a motion compensator 60 which,in turn, compensates the delayed frame signal for movement. A firstadder 8 a produces a difference signal representing the differencebetween the present frame and the delayed, motion-compensated frame. ADCT coder 10 DCT-codes the difference signal. The DCT coded image signalis quantized by a quantizer 20 and then dequantized by a dequantizer 21.The dequantized signal is supplied to a second adder 8 b, via IDCT 11,which adds it to the output of the motion compensator 11. This producesa signal corresponding to the original image signal.

[0022] The output of the motion compensator 50 is applied to the adders8 a, 8 b by refresh switches RSW2 and RSW1, respectively.

[0023] The quantized image signal is also supplied to a multi-scanner 80which scans it according to a plurality of predetermined patterns.

[0024] A scanner pattern selector 90 selects the scanning pattern whichproduces the minimum number of bits to represent the current sub-block.The scanning pattern selector also produces selection data whichidentifies the selected scanning pattern.

[0025] The image signal output by the scanning pattern selector 90 isvariable length coded by a variable length coder 60. The variable lengthcoder 60 compresses the image signal output by the scanning patternselector 90. The variable length coder 60 operates such that a largeproportion of the data samples are each represented by a small number ofbits while a small proportion of the data samples are each representedby a large number of bits.

[0026] When a discrete cosine transformed image signal is quantized andrunlength coded, the number of “0”s is increased over all, while thenumber of “0”s decreases as the magnitude of the signal increases.Accordingly, data compression is achieved because “0” can be representedby only a few bits and “255” can be represented by a relatively largenumber of bits.

[0027] Both the variable length coded signal and the selection data aresupplied to a multiplexer MUX1 which multiplexes the variable lengthcoded signal and the selection data, and optionally additionalinformation such as teletext.

[0028] Since the variable length coded signal has data words ofdifferent lengths, a transfer buffer 70 is employed to temporarily storethe multiplexed signal and output it at a constant rate.

[0029] The original image signal is reconstructed at a remote station byperforming the appropriate inverse scanning of the runlength codedsignal in accordance with the multiplexed scanning pattern selectiondata.

[0030]FIGS. 3A to 3H show possible scanning patterns employed by themulti-scanner 80. Additional scanning patterns will be apparent to thoseskilled in the art. However, if the number of patterns becomes toolarge, the coding efficiency is degraded as the selection data wordbecomes longer.

[0031] As described above, according to the present invention, thequantized image signal is scanned according to various scanningpatterns, and then the most efficient pattern is selected. A suitablemeasure of efficiency is the number of bits required to runlength codethe image signal.

What is claimed is:
 1. A signal compressing system, comprising: codingmeans for scanning an input signal according to a plurality of differentscanning patterns to provide coded versions thereof; and selection meansfor selecting that one of said scanning patterns which producesefficient coding according to a predetermined criterion and outputting ascanning pattern signal identifying the selected scanning pattern.
 2. Asystem according to claim 1, wherein the coding means codes the inputsignal according to a runlength coding regime.
 3. A system according toclaim 1, further comprising a variable length coder to variable lengthcode the coded signal which is produced by scanning according to theselected scanning pattern.
 4. A system according to claim 1, furthercomprising discrete cosine transformer means to produce said inputsignal.
 5. A system according to claim 4, wherein said transformer meansis a motion-compensated interframe adaptive discrete cosine transformer.6. An image data compressing system comprising: means for obtaining adifference between the present frame and a preceding motion-compensatedframe of an image signal; means for coding the difference by discretecosine transform coding and quantizing the discrete cosine transformcoded image signal difference and inverse discrete cosine transformcoding the dequantized image signal; means for compensating the motionof the image signal; means for coding the quantized image signal byvariable length coding; a selector for selecting an appropriate imagescanning pattern from at least one of a plurality of image scanningpatterns; a multi-scanner for scanning the quantized image signal byvarious scanning patterns; a scanning mode selector for selecting ascanning mode in which a number of bits produced from a start to an endof a data sub-block is minimized, the variable length coder for codingthe image signal output of the scanning mode selector by way of variablelength coding; and a multiplexer for multiplexing and outputting thevariable length coded signal and the scanning pattern selecting signaloutput by the scanning pattern selector.
 7. A system according to claim2, further comprising a variable length coder to variable length codethe coded signal which is produced by scanning according to the selectedscanning pattern.
 8. A system according to claim 2, further comprisingdiscrete cosine transformer means to produce said input signal.
 9. Asystem according to claim 3, further comprising discrete cosinetransformer means to produce said input signal.